Since the invention of the "bottom-pour" ladle, more than one hundred years ago, nozzles have been "set" in nozzle blocks by smearing wet fireclay on the nozzle and pushing the nozzle into place in the nozzle block. Then the ladle is heated with a gas or oil flame until the fireclay is dried and has set. This heating consumes many hours. It is imperative that the fireclay be completely dry, as any moisture trapped under molten steel or other hot molten metal will instantly flash into high pressure steam which can explode dangerously, throwing hot molten metal in all directions.
Although fireclay has and is being used extensively for setting nozzles, its use has other disadvantages. The thermal bond or "set" that it forms is weak and occasionally breaks during teeming. The nozzle then floats to the top surface of the molten metal which rushes out through the nozzles block in a disastrously uncontrollable stream which cannot be poured into a mold or tundish and so must be discarded as scrap. In addition, such uncontrolled pouring is extremely hazardous to personnel working in the plant.
Wet "air-setting" refractories are used to a limited degree to set a nozzle in a nozzle block. These are smeared on the nozzle before inserting it into the nozzle block and also must be carefully fired to remove the last traces of moisture before using the nozzle in a pour. These refractories contain chemical bonds, typically liquid sodium silicate, which when dried forms a strong bond. Consequently the nozzle is strongly cemented to the nozzle block from top to bottom. Punching the nozzle out after using it results in severe damage to the nozzle block which must be replaced after one or only a few pours. As nozzle blocks are large and heavy, they are expensive and time-consuming to remove and replace, air-setting mortars are not generally used for nozzle-setting.
Accordingly, one of the principal objects of the present invention is to provide rapid heat-setting refractories which can be used to hold in place nozzles employed for pouring steel or other molten metals. These refractories are granular and dry. They may be poured into the annular space between nozzles and their nozzle blocks which are normally located in the bottom of the ladles, tundishes or other vessels used for holding and pouring hot molten metal. It is then not necessary to heat the refractory to high temperatures before use as the heat from molten metal tapped into even a cold ladle hardens the refractory, so that the refractory, nozzle and nozzle block are almost instantly cemented together. The rapidity of this cementing action prevents the nozzle, usually made of fireclay or other ceramic material which has considerably lower specific gravity than molten metals, such as steel, from floating out of the nozzle block when the stopper-rod is raised for "teeming" or pouring the steel through the nozzle.
An additional advantage of using these dry, heat-setting refractories is that only the top few inches of the nozzle are cemented to the nozzle block. Thus after the heat or batch of molten metal has been poured the used nozzle can be easily punched out with minimum damage to the nozzle block. Nozzles are generally used only once. Nozzle blocks, if not damaged when the used nozzles are punched out, can last through the full life of the ladle lining which, in typical steel plant use may be fifteen to thirty pours or more.
Thus it is another principal object of this invention to provide a reliable dry heat setting refractory which allows a nozzle to be removed from a nozzle block after use without damaging the nozzle block.
It is still another major object of this invention to provide a quick and inexpensive method of setting nozzles. This method requires less skill to be used successfully and it saves considerable time and energy because it does not require any preheating prior to use in pouring hot molten metals, such as steel or other substances.
Our method does not require the hours of preheating presently necessary to dry fireclay and other refractories currently in use. Our method also provides a stronger bond than does fireclay so that accidents resulting from inadvertent breaking of the bond between the nozzle and nozzle block are obviated.
These and other objects and advantages will become apparent hereinafter.